1. Field of the Invention
The present invention relates to a bi-morph or uni-morph type piezoelectric or electrostrictive actuator used as or for a displacement-controllable element, a solid element motor, an ink jet ejector, a relay, a switching element, a camera shutter, a print head, a pump, a fan or blower, and other components or devices. The term xe2x80x9cactuatorxe2x80x9d used herein is a member capable of transducing or converting an electric energy into a mechanical force, displacement or strain.
2. Discussion of the Prior Art
Recently, an element whose displacement can be controlled has been widely used and increasingly needed in the fields of optics and precision positioning or machining operations, for example, for adjusting or changing an optical path length or the position of a member or component of a device, on the order of fractions of a micron (xcexcm). To meet this need, there have been proposed and developed various piezoelectric or electrostrictive actuators utilizing a piezoelectric or electrostrictive material such as a ferroelectric material, which exhibits the reverse or converse piezoelectric effect or the electrostrictive effect, in which the application of a voltage or electric field to such a piezoelectric or electrostrictive material produces a mechanical displacement.
Conventionally, the piezoelectric/electrostrictive actuator is structurally classified into a mono-morph type, a uni-morph type, a bi-morph type and a lamination type. The mono-morph, uni-morph and bi-morph types provide a relatively large amount of bending or flexural displacement or deflection or distortion owing to the transverse mode of converse piezoelectric or electrostrictive effect, namely, due to the strain perpendicular to the direction of the electric field produced upon application of a voltage. However these types suffer from inherent problems such as a small magnitude of a force generated, a low response speed, a low level of electro-mechanical conversion efficiency, and a low degree of operating reliability due to the use of an adhesive for bonding the component layers. On the other hand, the lamination type utilizes the longitudinal mode of converse piezoelectric or electrostrictive effect, namely, the strain parallel to the direction of the electric field, and therefore assures a large magnitude of the generated force, a high response speed, and a high level of electro-mechanical conversion efficiency. However, the lamination type suffers from an inherent problem that the amount of displacement produced is relatively small.
The conventional piezoelectric/electrostrictive actuator of the uni-morph or bi-morph type also suffers from relatively low operating reliability, which arises from the use of a bonding agent for bonding together the component sheets or plates of the actuator such as a piezoelectric/electrostrictive element.
Thus, the conventional piezoelectric or electrostrictive actuators have drawbacks as well as advantages, and suffer from some problems that should be solved.
It is accordingly a first object of the present invention to provide a piezoelectric/electrostrictive actuator of uni-morph or bi-morph type which does not use a bonding adhesive or cement and which undergoes a sufficient amount of displacement by application of a relatively low voltage, with an improved response to the applied voltage.
Another object of the invention is to provide such a piezoelectric/electrostrictive actuator wherein piezoelectric/electrostrictive actuator units are formed with high integration density on a substrate or supports
The above objects may be achieved according to the principle of the present invention, which provides a piezoelectric/electrostrictive actuator comprising a ceramic substrate, and at least one piezoelectric/electrostrictive actuator unit formed on at least a portion of at least one surface of the substrate. Each piezoelectric/electrostrictive actuator unit comprises a first electrode film, a piezoelectric or electrostrictive film and a second electrode film which are laminated in the order of description.
The piezoelectric/electrostrictive actuator of this invention wherein each piezoelectric/electrostrictive actuator unit consists of a laminar structure as described above provides a large amount of displacement by application of a relative low voltage applied thereto, with a high response to the applied voltage. Further, the laminar piezoelectric/electrostrictive actuator units may be formed with improved integration density on the substrate. Although the piezoelectric/electrostrictive actuator of the present invention which includes the laminated films integrally formed on the substrate is more or less similar in construction to the conventional bulk type laminar actuator, the present actuator is capable of undergoing a sufficient amount of flexural or bending displacement or distortion owing to the transverse mode of converse piezoelectric or electrostrictive effect produced upon application of an electric field, and generating an accordingly large force, while assuring improved operating response.
Further, the laminar structure including the electrode films and piezoelectric/electrostrictive film are integrally laminated on the substrate, without a bonding adhesive as conventionally used for bonding thin component sheets of the known actuator of the uni-morph or bi-morph type. Consequently, the present piezoelectric/electrostrictive actuator has improved operating reliability for a prolonged period of use, and the displacement to be produced by the actuator is subject to a minimum amount of drift.
The laminar structure according to the present invention permits the piezoelectric/electrostrictive actuator units to be easily formed with a relatively high density on the same surface of the substrate.
According to a finding of the applicants, for obtaining a large amount of flexural or bending displacement and the accordingly large magnitude of the force generated, the thickness of the present actuator is preferably 300 xcexcm or less, and more preferably 150 xcexcm or less, and the bending strength of the ceramic substrate is preferably at least 1200 kgf/cm2, and more preferably at least 1500 kgf/cm2.